Field of the Invention
The present invention relates to a lighting system comprising a tube light with an improved LED array capable of producing light within at least two desired predetermined color temperature ranges.
Description of the Related Art
Fluorescent light bulbs or lamps have been used for a long time for various artificial lighting purposes, from residential to commercial lighting. Fluorescent lamps are gas-discharge lamps that use electricity to excite mercury vapor to produce short-wave ultraviolet light that then causes a phosphor to fluoresce, producing visible light. Many fluorescent bulbs are made in tubular form which contains the mercury vapor. As a result, larger fluorescent lamps require large elongated tube lamps to produce the desired amount of light.
While larger fluorescent lamps have been used mostly in commercial buildings or institutional buildings, they also have applications in the lighting industry such as TV, stage, auditorium, and/or film studio use, and/or other venues. However, fluorescent lamps must be used with caution in the lighting industry as the color temperature of fluorescent lamps may create unwanted visual effects for the viewer. Color temperature is a characteristic of visible light measured by the temperature of an ideal black body radiator that radiates light of comparable hue to that of the light source. Color temperature is conventionally stated in the unit of absolute temperature, Kelvin (K). Color temperatures over 5,000 K are considered “cool” colors (blue-ish white), while lower color temperatures of 2,700 to 3,300 are considered “warm” colors (yellowish white through red).
The spectrum of light emitted from a fluorescent lamp is the combination of light directly emitted by mercury vapor, and light emitted by the phosphorescent coating. The spectral lines from the mercury emission and the phosphorescence effect give a combined distribution of light that is different from those produced by incandescent sources. Colored objects are perceived differently under light sources with differing spectral distributions. For example, some people find the color rendition produced by some fluorescent lamps to be harsh and displeasing, sometimes giving a greenish hue to skin tones giving people a sickly or unhealthy appearance. In addition, when used for lighting TV, studio, or film productions, the color temperature of the lighting often may need to be changed in order to match the scene or mood of the production. For example, recreating a scene taking place under sunlight with blue skies may require a color temperature of 9000 to 12000 Kelvin (K), while a scene taking place at sunrise or sunset may require a lighting color temperature of 3200 K. The two most frequently used and desired color temperature ranges in the lighting industry for stage and set lighting have been found to be 3050 to 3300 K for tungsten (warm white), and 5400 to 5600 K for daylight white. These ranges represent ideal color temperature ranges for producing ideal lighting for TV, photography and film studio scenarios.
In such uses where accurate and suitable lighting color temperature is vital, lighting “gels” are often used in conjunction with fluorescent lamps to produce the desired color temperature. These lighting gels often consist of colored tube shaped sleeves made from a semi-transparent material to give the light the desired color effect. Although allowing for modification of the color temperature of light, techniques such as using color gels do not provide an easy method to change the lighting and so cause significant delays in production. For example, if shooting a daytime scene, production workers would need to manually remove and replace all of the colored gels on the fluorescent lamps being used, often a daunting task when faced with several banks of lamps, each bank consisting of numerous individual fluorescent lamps. Or without colored gels, a lighting crew must continually change the fluorescent lamps between daylight white (or day white) colored lamps and tungsten (or warm white) colored lamps, or if desired, other types of white/light colored lamps.
Alternatively, LED (light emitting diode) lighting has been developed and has recently gained popularity. Since LEDs use very little energy and have a relatively long life, in recent years it has been popular to replace existing fluorescent bulbs with LEDs. LEDs present many advantages over incandescent or fluorescent light sources including lower energy consumption, longer lifetime, improved physical robustness, smaller size, and faster switching. There are two primary types of LED lighting used to create white light. One is to use individual LEDs that emit three primary colors (red, green, and blue) and mix the colors to form white light. The other is to use a phosphor material to convert monochromatic light from a blue or ultraviolet LED to broad-spectrum white light, also referred to as phosphor based LEDs.
In order to match the tubular form of a fluorescent bulb, arrays of LEDs may be placed within a tube having the same form factor as a fluorescent lamp, such as a T8 or T12 size fluorescent bulb. One such bulb is made by Dialight and is called DuroSite™. For example, in size T8, the bulb in one form uses SMD LEDs in a four foot long tube and provides 1500 Lumens of Natural White light, using 17 Watts, 300 LEDs, with 90V-277V, and is ETL/UL Approved. However, such existing products cannot provide a lighting solution to create two different predetermined color temperature light outputs suitable for use in the stage lighting industry, for uses such as TV, stage, photography and studio lighting. Sufficient intensity of the light is preferably at least 1000 lux for such an application.
In U.S. Pat. No. 8,203,260 to Li et al discloses an LED light made in a form factor of a fluorescent light and having color temperature which is tunable by blending adjacent pairs of LEDs by dimming one or both LEDs a customized amount to achieve the desired color. The control is complex and the temperature of the cold light is relatively high. The lighting is intended for street lights, vehicle headlights, and/or for other lights subject to moisture, fog, dust or smoke situations. Therefore, a fog or moisture sensor or other sensor is preferably used with the device. Since the drive current to each of the different color LEDs must be reduced to achieve the desired blend of light, the intensity is not only reduced but is expected to vary quite a bit from color to color. There is no single source mode, and the light output is not suitable for studio use.
What is desired is a lighting solution suitable for the lighting industry implementing the advantages of LED lights which allows for evenly dispersed light controllable within specific color temperature parameters without the need to physically switch out colored gels or lamp modules to achieve the desired color temperature light. It is also desirable to maintain the shape and interface of a traditional fluorescent lamp so as to allow maximum usability in the lighting industry without requiring expensive and time consuming equipment overhaul and upgrades.